Bigeye tuna live in tropical and warm temperate waters of the Atlantic, Pacific and Indian oceans. They are pelagic and exhibit several dispersion patterns. The Western and Central Pacific Ocean and the Indian Ocean bigeye are each considered single and separate stocks; although considerable mixing occurs, Western and Central Pacific Ocean and Eastern Pacific Ocean bigeye tuna populations are assessed separately for management purposes.
Bigeye tuna form free schools or may swim associated with floating objects such as logs. Juvenile bigeye will form schools with juvenile yellowfin and skipjack tunas. Bigeye tuna tolerate warmer and deeper waters and lower oxygen and salinity levels than other tropical tunas. They may live to at least 15 years of age. They grow more slowly than yellowfin tuna, have lower natural mortality, and are less abundant.
Bigeye tuna is important in commercial fisheries around the world, accounting for nearly 10% of the world’s catch of major tunas. In the Central and Western Pacific Ocean, 6% of the tuna caught are bigeye and, in the Indian Ocean, 12% are bigeye. Juveniles are caught by both surface gears such as purse seines and, in the Indian Ocean, by gill nets. As valuable adult fish, they are caught by longline and other gears. They are a principal target species of both the large, distant-water longliners from Japan, Korea, China, Taiwan and the smaller, fresh sashimi longliners based in several Pacific Island countries.
SUSTAINABILITY AND MANAGEMENT
The bigeye tuna stock of the Western and Central Pacific is overfished and subject to overfishing; the Indian Ocean bigeye stock is not overfished, nor subject to overfishing. The catch of juvenile bigeye in surface fisheries that target skipjack and yellowfin tuna, e.g., purse seine and gillnet fisheries, is increasing, thus decreasing the biomass of adults in the deeper water longline fisheries and the maximum sustainable yield of the stocks.
Bigeye tuna resources are managed by the Western and Central Pacific Fisheries Commission (WCPFC), the Indian Ocean Tuna Commission (IOTC), and national governments. Sub-regional fishing interest groups, international environmental organisations and market controls also have a strong influence on the governance of bigeye tuna fisheries.
The meat of bigeye tuna is highly prized and is processed into sashimi in Japan (and western countries). Bigeye is marketed mainly in canned, frozen, or fresh forms. Prices paid for both frozen and fresh product on the Japanese sashimi market are the highest among all the tropical tunas.
As food, bigeye is a very good source of low-fat protein and is low in sodium, but has a moderate level of cholesterol. Fat content in bigeye tuna is higher than in other tuna species, yet it is a good choice for low-fat diets.
ECUSYSTEM AND CLIMATE
Bycatch of fishing for bigeye tuna and other pelagic species includes bigeye tuna juveniles, and also sea turtles, sharks, seabirds and other marine fish species and is a significant environmental issue. Among all fishing gears used for bigeye tuna, longlines and gillnets have the greatest bycatch rates.
Longline and purse seine fishing are among the most energy intensive fishing operations as measured by greenhouse gases produced per tonne of fish landed. Also, unless strictly managed, fish canneries may have negative effects on surrounding land and sea environments and the resources they support.
The area of suitable bigeye tuna habitat changes with seasons and with inter-annual climate variability and this is reflected in the catches of bigeye tuna. In the Western and Central Pacific Ocean, the El Niño Southern Oscillation events affect catches of bigeye tuna which are higher during the warmer El Niño period and lower during the cooler La Nina periods.
Global warming affects the distribution and catchability of bigeye tuna stocks which are sensitive to changes in oceanic circulation, the stratification of the water column and water temperature and density.
WILD HARVEST FISHERIES
All bigeye tuna production is from wild harvest fisheries. Bigeye tuna is a moderately fast-growing, widely distributed and very fecund species. It is heavily fished by many different methods and, despite its high productivity, its stocks face future challenges due to a high demand. Stocks in the Western and Central Pacific Ocean (WCPO) are overfished; stocks in the Indian Ocean (IO) are currently not overfished. In both oceans areas, the problem of bycatch from longline, gillnets (IO), purse seine fishing with drifting fish aggregating devices (FADs), and the impact of pole and line fishing on baitfish stocks cause environmental problems that are being addressed by several conservation management measures, but the effects of these measures are not considered adequately monitored except in the case of the WCPO purse seine fishery.
IUCN Red List Status
Vulnerable (globally) http://www.iucnredlist.org/details/21859/0
Because the maximum sustainable yield (MSY) of the Western and Central Pacific bigeye tuna stock represents about 20% of the global populations, bigeye tuna is listed as 'vulnerable' globally.
State of the Stocks and Impacts of Fishing
The bigeye tuna resources of the WCPO are overfished and management measures may not be adequate to prevent overfishing. Most of the catch is taken by fishing methods that entail significant bycatch (longlines and surface purse seining on fish aggregating devices (FADs), or, in the case of the small amount of bigeye tuna taken by pole and line, methods that may negatively impact local baitfish species. Monitoring of purse seine fishing is comprehensive and adequate. Monitoring of longline fishing is not as comprehensive as that for purse seine fishing, having lower coverage of logsheet data submitted to the WCPFC and lower observer coverage of fishing trips. However the vessel monitoring system (VMS) coverage of longline fishing, however, is close to 100%.
The bigeye tuna resources of the IO are not overfished, nor subject to overfishing. The majority of the catch is taken by longline, purse seine around FADs and gillnet. These are methods with significant bycatch problems.
The following bigeye tuna stock status information, by ocean, is drawn from the scientific reports of the regional fisheries management organisations and from the International Seafood Sustainability Foundation’s (ISSF) overview of stock status, rankings of management measures and impacts of fishing on bycatch (Status of the Stocks Technical Report).
Orange - B < BMSY. The stock has been subjected to overfishing for more than 10 years, and is now overfished. Spawning biomass is below the Limit Reference Point adopted by WCPFC.
Orange - F > FMSY. The WCPFC management measures in place appear to be
insufficient to end overfishing in the short term.
Orange – 44% of the catch is made by longlining. Several mitigation measures are in place (sharks, turtles, sea birds). Monitoring is deficient.
– 38% of the catch is made by purse seining on floating objects (including FADs). Several bycatch mitigation measures are in place (turtles, sharks). There is 100% observer coverage on part of the purse seine fleet.
Green – 6% of the catch is made with purse seining on free schools, with little impact on non-target species.
Yellow - 3% of the catch is made by pole-and-line fishing, with unknown impacts on baitfish stocks.
IO BIGEYE TUNA
– 56% of the catch is made by longlining. Several mitigation measures are in place (sharks, turtles, sea birds). Monitoring is deficient.
– 21% of the catch is made by purse seining on floating objects (including FADs). Several bycatch mitigation measures are in place (turtles, sharks).
Orange – 16% of the catch is made by other gears such as gillnet. There is poor reporting by these fisheries which are thought to have substantial amounts of bycatch.
Green - 7% of the catch is made with purse seining on free schools, with little impact on non-target species.
Certificates for sustainability of wild harvest fishery
Marine Stewardship Council (www.msc.org)
No bigeye tuna fisheries are certified.
Friend of the Sea does not certify fisheries, but audits and certifies companies in the fish supply chains to adopt selective fishing methods, reduce ecosystem impact and manage within maximum sustainable yield. The certification also deals with quality standards for energy efficiency and social accountability. A list of currently certified fleets for bigeye fishing in the Indian Ocean can be found through this link. and social accountability.
Several conservation and sustainable/fair food organizations also promote sustainable tuna campaigns, e.g., see the Pew Charitable Trusts Global Tuna Conservation campaign.
The status of bigeye tuna stocks is difficult to assess because each stock is harvested by many different fishing gears, over a wide geographic area with each gear type tending to catch fish of a different size range. Longline fishing mainly harvests adult bigeye tuna whereas purse seines and gillnets harvest a wide size range of bigeye tuna, including many juveniles.
Compared to skipjack and yellowfin tuna stocks, those of bigeye tuna are more vulnerable to overfishing and take longer to recover after a population decline because they are relatively long-lived and mature later than these other tunas. The large and increasing catches of bigeye juveniles by surface fisheries are reducing the size of the spawning stock of large fish caught in the deeper waters by longlines, and reducing the maximum sustainable yield of the whole fishery.
Fisheries catch data, which are essential to bigeye tuna assessments, have several shortcomings. In particular, reporting of bigeye tuna catches is inconsistent among fleets and gears. For some gear types, such as gillnets and those used in artisanal fishing, reporting of catch and effort is limited, e.g., despite their importance, the catches of bigeye tuna in Indonesia, Philippines, and Vietnam are not fully monitored. Bigeye tuna catches are under-reported for several gear types, especially purse seines, because juvenile bigeye join schools and are harvested with other tuna species of similar size, especially skipjack and yellowfin tuna. Log sheets from purse seine fisheries tend to be biased towards recording most small tunas as skipjack. Observer sampling in port and at sea has revealed under-reporting of yellowfin and bigeye of up to 15% (for sets associated with floating objects). Such under-recording of juvenile yellowfin and bigeye tuna occurs both in the WCPO and the IO fisheries and the logbook estimates are adjusted using port - or at sea - samples of fish to help reduce the bias. Difficulties in distinguishing juvenile bigeye from juvenile yellowfin tuna also cause data problems (see Biology).
Western and Central Pacific Ocean
For bigeye tuna in the WCPO, stock assessment and data management services are provided by the Oceanic Fisheries Programme of the Secretariat of the Pacific Community (SPC) and reviewed by the Scientific Committee of the Western and Central Pacific Fisheries Commission (WCPFC). Bigeye assessments are based on catch, effort, fish size and tagging data from the major component fisheries – longline and purse seine fleets - and defined fishing regions of the management area of the WCPFC. Corrections and adjustments are made in the assessment models to account for the estimates of catch composition by species and biases in the monitoring data. Increasing attention is being paid to analyses of data from the fisheries conducted in the intensively fished Indonesian and Philippine waters. The Scientific Advisory Committee of the ISSF takes the WCPFC stock assessments, plus other reliable information, and makes their sustainability assessments based on the estimates of stock abundance, fishing mortality and environmental impact.
Based on annual recent harvests of about 145,000 tonnes, bigeye stock assessment for the Western and Central Pacific Convention Area in 2014 indicated that overfishing is occurring and to rebuild the spawning stock biomass to above the limit reference point requires that fishing be reduced. The excessive fishing and the increased catch of juvenile bigeye tuna, especially in the tropics, reduced the potential yield of the WCPO bigeye tuna stock. The estimated MSY is 108,500 tonnes, but this is still subject to uncertainty due to missing data, especially longline data from some fleets.
Longlines take about 44% of the bigeye catch, and purse seines take about 47%, with pole-and-line; handline and other gears taking small shares. In 2013, the record purse seine catch of bigeye tuna exceeded that of longlines for the first time. The purse seine and other surface fisheries have slightly greater impact on bigeye stocks than does the longline fisheries. The purse seine and Philippines and Indonesian domestic fisheries impact the western Pacific fishery around the equator, and the Japanese coastal pole-and-line and purse-seine fisheries impact the bigeye fishery in the north.
For bigeye tuna in the IO, the stock is assessed by the Scientific Committee of the Indian Ocean Tuna Commission (IOTC). The Scientific Advisory Committee of the ISSF takes the IOTC stock assessments, plus other reliable information, to make their sustainability assessments based on the IOTC estimates of stock abundance, fishing mortality and environmental impact. Tag recoveries suggest that bigeye tuna in the Indian Ocean belong to a single stock.
Indian Ocean bigeye tuna stock is not overfished and is not experiencing overfishing. The MSY for the Indian Ocean bigeye stock size is 132,000 tonnes, compared to a recent average of 106,000 tonnes. Catches increased after 2011, however, as the piracy threat in the western Indian Ocean decreased. Stock estimates for the IO are compromised by the lack of detailed catch statistics from some coastal fisheries, the gillnet fisheries of Iran, Pakistan and Sri Lanka and some industrial longline fleets (e.g. from India, Philippines).
Bigeye tuna fisheries are managed by regional fisheries management organizations (RFMOs) and by national governments. Reaching agreement on management measures is difficult due to competing interests of countries and fleets and preferences for different types of management choices, e.g., controls on the number of licenses, total allowable catch limits, vessel day limits, and restricting access to fishing areas.
As for the stock assessments, the management of bigeye tuna fisheries is complicated by the mix of gears and fleets exploiting the stocks in both oceans, and problems in under-reporting of catches of bigeye (and yellowfin), especially in purse seine fisheries.
Industrial tuna fisheries are managed by the Western and Central Pacific Fisheries Commission (WCPFC) in the WCPO, the Indian Ocean Tuna Commission (IOTC) in the IO, and the Inter-American Tropical Tuna Commission (IATTC) in the Eastern Pacific Ocean (EPO). There is some overlap between the WCPFC and IATTC Convention Areas with respect to management of bigeye tuna. The RFMOs meet annually to consider and endorse recommended management actions. [See Slide Show for convention area maps]
Regional associations of countries are increasingly influential in tuna fisheries management, more so in the WCPO than the IO. Individual island countries also manage their tuna resources, through national tuna management plans.
Each of the RFMOs has a scientific committee that provides advice on stock status, monitoring and management implications, using their own and additional scientific expertise. In the case of the WCPFC. SPC is the data management service provider, and holds all of the data used in assessments. WCPFC has the parts of this that are designated as WCPFC data.
Through negotiations, the RFMOs recommend management measures (‘Conservation and Management Measures’ or CMMs) aimed at securing the sustainability of tuna stocks and, more recently, bycatch stocks and the marine environment. However, because the RFMOs use consensus-based decision-making, it is increasingly difficult for agreement to be reached between science, politics and economics on the implementation of effective stock management measures.
In the European Union countries, which are important tuna markets for WCPO and IO tuna, regulations against illegal, unreported and unregulated (IUU) fishing vessels (Council Regulation (EC) No. 1005/2008 and Commission Regulation (EU) No 468/2010) act, in effect, as management drivers.
In addition, campaigns by international environment organizations, such as Greenpeace, the Pew Environment Group and the World Wide Fund for Nature (WWF), advocate against the catch of juvenile bigeye and yellowfin tuna, especially by purse seiners in association with drifting FADs. These campaigns have led to some marketing chains (in Australia, UK, USA) imposing bans or foreshadowing bans on canned tuna harvested around FADs.
Western and Central Pacific Ocean
To achieve sustainable fishing on bigeye tuna, the WCPFC Scientific Committee has recommended that the fishing mortality rate for the bigeye stock needs to be reduced to the target rate of FMSY, i.e., a reduction of 36% relative to the average 2008-2011 level. If the mortality of small bigeye during purse seine operations can be reduced, greater overall yields could be achieved, the average MSY would increase, and the total value of the catch would be higher because larger fish fetch better prices than juveniles. ISSF and other organisations are now engaged in developing purse seine methods designed to capture of fewer bigeye tuna to help achieve these outcomes.
While trying to reduce fishing on bigeye (and yellowfin) tuna, management agencies have to deal with the economic losses that the purse seine fisheries primarily catching skipjack tuna would suffer. With a view to controlling overfishing on bigeye in the face of increasing fishing pressures and fishing fleet dynamics, the WCPFC continues to develop and encourage implementation of annually revised Conservation and Management Measures (CMM). CMM 2014-01 and its precursors contain articles to control skipjack, yellowfin and bigeye fishing rates by: management of fishing on FADs and floating objects including seasonal closures, effort controls, high seas controls, retention policies, compliance and observer arrangements, and bigeye longline catch limits by fishing flag states. So far, little progress is being made to achieve the target of reducing bigeye fishing mortality to the sustainable level by 2017.
A subset of WCPFC member countries, the Parties to the Nauru Agreement (PNA), also place limits on purse-seine fishing effort within their Exclusive Economic Zones (EEZ) through a ‘vessel day scheme’ (VDS) that only licenses those purse-seine vessels that do not fish in the high seas between 100Nand 200S, including the two tropical high-seas pockets within their region.
The benefits of any bigeye conservation measures are expected to take 10-20 years to be realised and, over that period, the projected benefits would be moderated by the effects of climate changes.
Pacific island countries also have to balance domestic development aims for national tuna fishing and onshore processing facilities with sustainable use of tuna resources. Groups of countries have been formed to help foster collective country interests. Regional inter-governmental and industry organizations concerned with tuna in the WCPO are:
Pacific Islands Forum Fisheries Agency (FFA) (https://www.ffa.int/) - (member countries: Australia, Cook Islands, Federated States of Micronesia, Fiji, Kiribati, Marshall Islands, Nauru, New Zealand, Niue, Palau, Papua New Guinea, Samoa, Solomon Islands, Tokelau, Tonga, Tuvalu and Vanuatu)
Parties to the Nauru Agreement (PNA) () - (member countries: Federated States of Micronesia, Kiribati, Marshall Islands, Nauru, Palau, Papua New Guinea, Solomon Islands and Tuvalu). The influence of the PNA in tuna management in the WCPF Convention Area has been significant because, as a group, the zones of the member countries host significant yellowfin tuna resources.
Pacific Islands Tuna Industry Association (PITIA) (http://www.pitia.org/) - (member countries: Cook Islands, Federated States of Micronesia, Fiji, Kiribati, Marshall Islands, Nauru, Niue, Palau, Papua New Guinea, Solomon Islands, Tonga, Tuvalu and Vanuatu).
The annual IO catches of bigeye tuna are well below the maximum sustainable yield (MSY) level, and at present immediate management measures are not required. However, continued monitoring and improvement in data collection, reporting and analysis are required to reduce the uncertainty in assessments. The International Seafood Sustainability Foundation recommends that the fishery should be limited entry, accompanied by a closed vessel registry with the aim of reducing the number of fishing vessels targeting the stock.
As yet, the Indian Ocean Tuna Commission (IOTC) has not established particular conservation measures for bigeye. More generally, bigeye are subject to the Conservation and Management Measures (CMMs) of other species. These measures include providing catch data, limiting fishing capacity and keeping a record of licensed foreign and local fishing vessels, and catch retention. The main binding conservation measures requires that total catch should not exceed 110,000 tonnes and that vessels longer than 24 m, and smaller vessels if they fish on the high seas, should respect a one-month closure for purse seiners and longliners in an area of size 10°x20°.
In addition to the IOTC management of bigeye and other tuna in the Indian Ocean, the Maldives Seafood Processors and Exporters Association and the Western Indian Ocean Fisheries Directors Forum represent the interests of industry or sub-regional country groups.
Although approval has been given for a yellowfin and bigeye tuna farm off Hawaii, it is not yet operational. Cage grow-out of bigeye is not conducted. The life-cycle of bigeye tuna has not been closed.
GUIDE TO FURTHER READING
For comments on tuna in IUCN Redlist, see Restrepo et al (2011)
For stock status updates, see the International Seafood Sustainability Foundation’s (ISSF) Status of the Stocks Technical Report, IOTC (2014) and IOTC Stock Status Dashboard (http://www.iotc.org/science/status-summary-species-tuna-and-tuna-species-under-iotc-mandate-well-other-species-impacted-iotc), SPC (2014).
For biological and fishery factors affecting bigeye tuna fishery assessments, see Babaran (2006), Colette et al. (2011), Hampton & Williams (2011), Lawson (2010) and Miyake et al. (2010).
For information on the Western and Central Pacific Ocean bigeye tuna assessments, see Harley et al. (2014), ISSF (2014), Langley et al. (2011), WCPFC (2014) and Willams & Terawasi (2014).
For information on the Indian Ocean bigeye tuna assessments, see IOTC (2014) and ISSF (2014).
For views on achieving effective regional management, see Hamilton et al. (2011) and Polacheck (2012).
For Western and Central Pacific Ocean bigeye tuna management arrangements, challenges and opportunities, including climate see Davies et al. (2011), Hamilton et al. (2011), Harley et al. (2009), ISSF (2014), Miyake et al. (2010), Restrepo et al. (2014) and Lehodey et al. (2011).
For Indian Ocean management see IOTC (2012) and ISSF (2012).
- Babaran RP. 2006. Payao fishing and its impacts to tuna stocks. A preliminary analysis. Western & Central Pacific Fisheries Commission, 2nd Scientific Committee Regular Session, 7-18 August 2006, Manila, Philippines, Paper FT-WP 7. 13 p.
Collette BB and 32 co-authors. 2011. High Value and Long Life—Double Jeopardy for Tunas and Billfishes. Science, 333: 291-292.
Davies N, S Hoyle, S Harley, A Langley, P Kleiber & J Hampton. 2011. Stock assessment of bigeye tuna in the Western and Central Pacific Ocean. Western and Central Pacific Fisheries Commission Scientific Committee Seventh Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia. WCPFC-SC7-2011/SA- WP-02. 133 p.
Hamilton A, A Lewis, MA McCoy, E Havice & L Campling. 2011. Market and industry dynamics in the global tuna supply chain. Forum Fisheries Agency, Honiara. 393 p.
Hampton, J & P Williams. 2011. Misreporting of purse seine catches of skipjack and yellowfin-bigeye on logsheets. WCPFC Scientific Committee Seventh Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia. Paper T-WP-02. 11 p.
Harley S, S Hoyle, A Langley, J Hampton & P Kleiber. 2009. Stock assessment of bigeye tuna in the Western and Central Pacific Ocean. Western and Central Pacific Fisheries Commission Scientific Committee Fifth Regular Session, 10-21 August 2009, Port Vila, Vanuatu. WCPFC-SC5-2009/SA-WP-4. 98 p.
Harley, S, N Davies, J Hampton, and S McKechnie. 2014. Stock assessment of bigeye tuna in the Western and Central Pacific Ocean. WCPFC-SC10-2014/SA-WP-01 Rev1 25 July, 115 p.
IOTC (Indian Ocean Tuna Commission). 2011. Executive Summary: status of the Indian Ocean bigeye tuna (Thunnus obesus) resource. IOTC-2011-SC14-09. 9 p.
IOTC (Indian Ocean Tuna Commission). 2012. Outcomes of the Fourteenth Session of the Scientific Committee relevant to the Second Technical Committee on allocation criteria. Indian Ocean Tuna Commission Second Technical Committee on Allocation Criteria, Maldives, 4–6 March 2012, IOTC–2012–TCAC02–04[E]. 11 p.
IOTC (Indian Ocean Tuna Commission). 2014. Report of the Seventeenth Session of the IOTC Scientific Committee Seychelles, 8–12 December 2014. IOTC–2014–SC17–R[E], 357 p.
ISSF (International Sustainable Seafood Foundation). 2012. ISSF position statement presented during the 16th Session of the Indian Ocean Tuna Commission in Fremantle, Australia 22-26 April, 2012. 2 p.
ISSF (International Seafood Sustainability Foundation). 2014. ISSF Tuna Stock Status Update, 2014: Status of the world fisheries for tuna. ISSF Technical Report 2014-09. International Seafood Sustainability Foundation, Washington, D.C., USA.
Langley, A, S Hoyle, & J Hampton. 2011. Stock assessment of yellowfin tuna in the Western Central Pacific Ocean. Western & Central Pacific Fisheries Commission 7th Scientific Committee Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia, Paper SA-WP-03 (Revision 1–03 August 2011). 135p.
Lawson, T. 2010. Update on the estimation of selectivity bias based on paired spill and grab samples collected by observers on purse seiners in the Western and Central Pacific Ocean. Sixth Regular Session of the Scientific Committee of the Western and Central Fisheries Commission, 10-19 August 2010, Nuku’alofa, Tonga. Working Paper SC6-WP02. 19p.
Lehodey P, J Hampton, RW Brill, S Nicol, I Senina, B Calmettes, HO Portner, L Bopp, T Ilyina, JD Bell and J Siebert. (2011). Vulnerability of oceanic fisheries in the tropical Pacific to climate change. In: Bell JD, Johnson JE, Hobday AJ (eds) Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change. Secretariat of the Pacific Community, Noumea, New Caledonia, pp. 433–492.
Miyake MP, P Guillotreau, CH Sun & G Ishimura. 2010. Recent developments in the tuna industry: stocks, fisheries, management, processing, trade and markets. FAO Fisheries and Aquaculture Technical Paper. No. 543. Rome, FAO. 125 p.
Polacheck T. 2012. Politics and independent scientific advice in RFMO processes: a case study of crossing boundaries. Marine Policy, 36: 132-141.
Restrepo VR, BB Collette & WW Fox. 2011. IUCN tuna assessments. 7 Jully 2011. Link
Restrepo V, L Dagorn, D Itano, A Justel-Rubio, F Forget and JD Filmalter. 2014 A summary of bycatch issues and ISSF mitigation initiatives to-date in purse seine fisheries, with emphasis on FADs. ISSF Technical Report 2014-1, International Seafood Sustainability Foundation, Washington DC, USA.
SPC (Secretariat for the Pacific Community). 2014. Evaluation of CMM 13-01. Western and Central Pacific Fisheries Commission, Commission Eleventh Regular Session, Apia, Samoa 1 - 5 December 2014. WCPFC11-2014-15, 8 p.
WCPFC (Western and Central Pacific Fisheries Commission). 2014. Summary Report of the Tenth regular session of the Scientific Committee. Majuro, Republic of the Marshall Islands, 6-14 August 2014.
Williams P and P Terawasi. 2014. Overview of tuna fisheries in the Western and Central Pacific Ocean, including economic conditions – 2013. WCPFC-SC10-2014/GN WP-1.
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All fishing gears have some level of environmental effect. Under the FAO Code of Conduct for Responsible Fishing, the fishing sector is expected to minimize its effects on the environment in order to sustain the resources and environment on which it relies. For bigeye tuna caught in surface and deep waters by a wide variety of fishing methods, bycatch is one of the most observable environmental effects, especially from fishing by longlines, gillnets and by purse seines on floating objects (including fish aggregating devices - FADs). In the case of purse seine vessels setting on FADs, bigeye tuna is not the target species and juvenile bigeye tuna are species are themselves regarded as bycatch (see - Sustainability).
Air and water pollution from fishing and fish processing are other environment concerns.
Ocean climate and global warming affect the distribution and catchability of bigeye stocks.
EFFECTS OF FISHING ON OTHER SPECIES
Bigeye tuna are caught by purse-seine, longline, pole-and-line and troll line in the Western and Central Pacific Ocean (WCPO), and by gill nets, longline, purse seine, pole and line, handline and troll line in the Indian Ocean (IO).
Fishing gear used to catch bigeye tuna does not come into contact with the seafloor and so does not directly affect the benthic environment.
Longline fishing targeting bigeye tuna (and albacore tuna) has a substantial bycatch of non-tuna species that can make up from more than half to two-thirds of the total catch, depending on the type of longline fishing. The main fish bycatch species in the WCPO include sharks, billfish, pelagic stingrays, and other finfish including moonfish (opah, Lampris guttatus), although their frequency in catches varies across the region.
Some longline vessels target sharks, especially when tunas are scarce. Sharks are targeted for their fins and meat. Longline crews often significantly top up their income from the sales of shark fins. Each year in the WCPO and IO, tens of thousands of individual sharks are caught and finned. In the WCPO, common bycatch sharks are: blue shark (Prionace glauca), silky shark (Carcharhinus falciformis), oceanic whitetip shark (Carcharhinus longimanus), mako sharks (Isurus spp), thresher sharks (Alopias spp), porbeagle shark (Lamna nasus), winghead hammerhead (Eusphyra blochii), scalloped hammerhead (Sphyrna corona), great hammerhead (Sphyrna mokarran) and smooth hammerhead (Sphyrna zygaena). Many shark species have experienced steep declines in catch in recent years, most likely due to high fishing mortality.
Conversely, sharks cause considerable damage to tuna on hooks in the longline fishery, and can reduce the value of the catch.
To reduce the catch and mortality of sharks, changes in longline gear are being used or investigated. These include changes in hook type and hook position in the water, replacing wire traces with nylon leaders and improving survival by better handling practices.
In the case of sea turtles, the loggerhead turtle is of most concern as bycatch in longline operations in the WCPO, although all species are at some risk. In the IO, all species of sea turtles are at risk of being caught by longlines.
Many species of seabirds are also caught by longlines in the WCPO, including especially large albatrosses in the higher latitudes. In the IO, breeding areas of species of albatross and petrel overlap extensively with the longline fishing grounds but records of bird catches are incomplete for many fleets. Mitigation methods are based on mapping the areas of greatest overlap of seabirds and fishing. Setting lines at night to avoid birds, weighting the lines for faster sinking and attaching streamers to keep the birds away are being encouraged to reduce bird mortality but more research is required to determine the most effective methods.
Marine mammal catches on longlines targeting bigeye tuna are not significant in most areas of the WCPO. In the IO, fishing for bigeye tuna in the northwest causes significant mortality of marine mammals.
Of the surface fisheries that catch juvenile bigeye, gill nets, used extensively in the IO, are of greatest concern for bycatch. This fishing is poorly monitored and traps a wide range of non-target species.
For purse-seine vessels targeting skipjack tuna, but which also catch juvenile bigeye tuna, the percentage of the catch comprised of non-tuna species is relatively low: 1.6% for nets set around FADs and 0.4% for sets on free-swimming schools not associated with FADs. In the WCPO purse seine fisheries, the bycatch of non-tuna species includes mainly silky shark, mackerel scad, mahi mahi (dolphin fish, Coryphaena hippurus), frigate mackerel, oceanic triggerfish and rainbow runner.
The bycatch from pole-and-line and troll fisheries is minimal. However, in the past when pole-and-line fishing was much more common than it is today, the stocks of the small pelagic fish species used as live bait were considered at risk of local depletion in some Pacific Island countries.
The Western and Central Pacific Fisheries Commission (WCPFC) and the Indian Ocean Tuna Commission (IOTC) have conservation and monitoring measures for bycatch mitigation and monitoring. Specific conservation and management measure address bycatch issues for sea turtles, sharks (including finning), sea birds, cetaceans, other finfish and reporting provisions to support bycatch research and monitoring. The International Seafood Sustainability Foundation (ISSF) conducts regionally specific by-catch mitigation training workshops for purse seine vessel skippers.
IMPACTS ON AIR AND WATER
All tuna fishing vessels rely on fossil fuel; their exhaust fumes and refrigerant gases contribute to greenhouse gases (GHG) emissions and thus global warming.
The estimated total carbon footprint of purse seine-caught tuna (all species) in 2009 was approximately 1,530 kg CO2 per tonne of tuna landed. The GHG emissions associated with catching tuna by purse-seine vessels, storing it on board and delivering whole fish to processing plants, are three times greater than the emissions stemming from the processing, packaging and transport of the resulting products.
The amount of fuel used to catch a tonne of tuna is greater for longline vessels than for purse-seine vessels. The carbon footprint of longline tuna products in increased further by the air freight required to deliver sashimi-grade tuna and other fresh tuna products to markets because GHG emissions are much higher for airfreight than for sea freight.
Bigeye tuna is a sought after species for sashimi and fresh rather than frozen product receives a premium price. Frozen and canned tuna transported by truck or container vessel have a lower carbon footprint than do fresh, chilled tuna transported by air.
For bigeye that are canned, the water, energy use and greenhouse gas emissions issues common to other canned tuna apply.
EFFECTS OF ENVIRONMENT ON BIGEYE
The life cycles of all tuna species depend on oceanic circulation: currents determine the location of spawning grounds, the dispersal and successful survival and growth of larvae, juveniles and adults, and the distribution of their prey. The availability of the nutrients in the tuna food web, and the location of water at suitable temperatures and levels of dissolved oxygen determine the tuna distribution and abundance.
In the WCPO, the El Niño Southern Oscillation (ENSO) is an oscillation between a warm (El Niño) and a cooler (La Niña) state. ENSO events have significant effects on bigeye tuna catches by surface and deep water fishing gears.
In the surface fisheries, catchability of bigeye tuna is lower during La Niña events when the thermocline is deeper and the surface layer of water is greater in volume, making bigeye less vulnerable to surface fishing gear. Bigeye tuna can tolerate lower levels of dissolved oxygen (O2) than other tunas and can feed at depths greater than 500 m. Longline catch rates of bigeye are also lower during La Nina events. The reverse occurs during El Niño events when the thermocline is shallower and surface temperatures higher. Surface fishery catch rates are higher during El Niño episodes and longline catch rates of bigeye tuna are also increased.
In the Eastern Indian Ocean off Java, ENSO events appear to have similar effects on bigeye tuna catch rates to those in the WCPO. In the IO, the Indian Ocean Index is a climate oscillation between a warmer and cooler state that better predicts warm and cold events in the Western Indian Ocean than do ENSO events. For bigeye longline catches in the IO, bigeye tuna catches tended to increase during warm events, although catch rates are affected by targeting practices.
EFFECTS OF CLIMATE CHANGE ON BIGEYE
Because of their mobility, bigeye tuna are likely to respond to increased sea surface temperatures and lower ambient O2 caused by the increased temperature by moving to areas within their preferred temperature ranges, both for spawning and feeding. Models that use projected changes in temperatures, currents, and food chains in the open ocean predict that future concentrations of bigeye are likely to be found further to the east than they are today. In the western equatorial Pacific, bigeye are likely to lose spawning grounds due to the projected high temperatures. The possible loss of equatorial spawning habitat may be compensated for by increased larval survival in the sub-tropics. Juvenile and adult fish, however, may have to contend with inferior habitat as sea surface temperatures rise and increase stratification of the water column, reducing availability of nutrients and prey, and as lower O2 concentrations occur near the surface.
Overall, by 2035, bigeye tuna catches are projected to decrease by a small amount (usually <5%), depending on the assumptions, in 17 of the 22 Pacific Island countries’ territories. By 2100, in some countries, larger declines of up to 30% are projected under some scenarios.
GUIDE TO FURTHER READING
Note: Details of all sources are given in References below
For tuna bycatch and discards in the IO tuna fisheries, see David Ardill and others (2011).
Shelley Clarke and others (2014) provided a global overview, by ocean, of longline bycatch and mitigation measures for sharks, sea turtles, seabirds, marine mammals and non-tuna finfish. For the WCPO, Shelton Harley and others (2014) reported on bycatch and non-tuna catch.
On shark catches in the WCPO tuna fisheries, see Shelley Clarke (2011), Shelley Clarke and others (2011) and Tim Lawson (2011). Mike McCoy & Bob Gillett (2005) provided insights into the shark targeting and importance of shark catches for crews on Chinese vessels. Makoto Peter Miyake and others (2010) reported on shark damage to tuna on longlines. The WCPFC’s Conservation and Management Measure (CMM) 2010-07 lists shark species of concern. For information on fishing gear modifications to reduce longline shark catch and bycatch see Don Bromhead and others (2013), Pew Marine Environment Group (2011), and Peter Ward and others (2007).
On baitfish for pole and line fishing in Solomon Islands and Fiji, see Steve Blaber and others (1993). For bycatch conservation and monitoring measures of the WCPFC, see https://www.wcpfc.int/conservation-and-management-measures, for IOTC see http://www.iotc.org/cmms; for a recent compendium of measures, see ISSF (2014).
Peter Tyedmers and Robert Parker (2011) provide a preliminary assessment of the impacts of bigeye tuna fishing and supply chain on air and water. The report from UNEP (2000) provided information on the environment impacts of tuna processing.
Effects of climate change on the foodwebs that support bigeye tuna and other species of tuna are reviewed by Robert Le Borgne and others (2011). For effects of climate change on bigeye tuna fish stocks see Patrick Lehodey and others (2011), who also projected catches under two future scenarios for greenhouse gas emissions. For ENSO effects on bigeye tuna catches in the EIO, see Mega Syamsuddin and others (2013), and for IO F. Ménard and colleagues.
- Ardill, D., D. Itano and R. Gillett. 2011. A Review of Bycatch and Discard Issues in Indian Ocean Tuna Fisheries. IOTC-2012-WPEB08-INF20. 44 p.
- Blaber, SJM, DA Milton & NJF Rawlinson. 1993. Tuna Baitfish in Fiji and Solomon Islands, proceedings of a workshop, Suva, Fiji, 17-18 Aug. 1993. Canberra: Australian Council for International Agricultural Research (ACIAR) Proceedings 52.
- Bromhead, D, J Rice, & S Harley. 2013. Analyses of the potential influence of four gear factors (leader type, hook type, “shark” lines and bait type) on shark catch rates in WCPO tuna longline fisheries. WCPFC-SC9-2013/EB-WP-02 rev 1.
- Clarke SC. 2011. A status snapshot of key shark species in the Western and Central Pacific and potential mitigation options. Western and Central Pacific Fisheries Commission Scientific Committee Seventh Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia. WCPFC–SC7–2011/EB–WP–04. 37 p. /
- Clarke S, S Harley, S Hoyle & J Rice. 2011. An indicator-based analysis of key shark species based on data held by SPC-OFP. Western and Central Pacific Fisheries Commission Scientific Committee Seventh Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia. WCPFC-SC7-2011/EB-WP-01 89 p.
- Clarke, S, M Sato, C Small, B Sullivan, Y Inoue, & D Ochi. 2014. Bycatch in longline fisheries for tuna and tuna-like species: a global review of status and mitigation measures. FAO Fisheries and Aquaculture Technical Paper No. 588. Rome, FAO. 199 p.
- Harley, S, P. Williams, S. Nicol and J. Hampton. 2014. The Western and Central Pacific Tuna Fishery: 2012 Overview and Status of Stocks. Secretariat to the Pacific Community, Oceanic Fisheries Programme. Tuna Fisheries Assessment Report 13, Noumea, New Caledonia. 31 p.
- ISSF (International Seafood Sustainability Foundation). 2014. ISSF Tuna Stock Status Update, 2014: Status of the world fisheries for tuna. ISSF Technical Report 2014-09. International Seafood Sustainability Foundation, Washington, D.C., USA.
- Lawson, T. 2011. Estimation of Catch Rates and Catches of Key Shark Species in Tuna Fisheries of the Western and Central Pacific Ocean Using Observer Data. Western and Central Pacific Fisheries Commission Scientific Committee Seventh Regular Session, 9-17 August 2011, Pohnpei, Federated States of Micronesia. WCPFC–SC7–2011 / EB–IP–02. 52 p.
- Lehodey P, J Hampton, RW Bril, S Nicol, I Senina, B Calmettes,HO Pörtner, L Bopp, T Ilyina, JD Bell & J Sibert. 2011. Vulnerability of oceanic fisheries in the tropical Pacific to climate change. pp 433-492, in JD Bell, JE Johnson & AJ Hobday (eds), Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change. Secretariat of the Pacific Community, Noumea, New Caledonia.
- Le Borgne, R., V Allain, SP Griffiths, RJ Matear, AD McKinnon, AJ Richardson & JW Young. 2011. Vulnerability of open ocean food webs in the tropical Pacific to climate change. pp 189-250, in JD Bell, JE Johnson & AJ Hobday (eds), Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change. Secretariat of the Pacific Community, Noumea, New Caledonia.
- McCoy MA & RD Gillett. 2005. Tuna longlining by China in the Pacific Islands: a description and considerations for increasing benefits to FFA member countries. FFA Report 05/13. Gillett, Preston & Associates Inc. 80 p.
- Ménard, F, F Marsac, E Bellier and B Cazelles. 2007. Climatic oscillations and tuna catch rates in the Indian Ocean: a wavelet approach to time series analysis. Fisheries Oceanography 16:95–104.
- Miyake MP, Guillotreau P, Sun CH & Ishimura G. 2010. Recent developments in the tuna industry: stocks, fisheries, management, processing, trade and markets. FAO Fisheries and Aquaculture Technical Paper. No. 543. Rome, FAO. 125 p.
- Pew Environment Group. 2011. Recommendations to Kobe III joint tuna RFMO meeting. http://www.pewtrusts.org/en/research-and-analysis/fact-sheets/2010/06/16/shark-bycatch-in-tuna-fisheries (accessed -5 February 2015).
- Syamsuddin, ML, SI Saitoh, T Hirawake, S Bachri, AB Harto. 2013. Effects of El Niño–Southern Oscillation events on catches of bigeye tuna (Thunnus obesus) in the eastern Indian Ocean off Java. Fishery Bulletin 111:175-188.
- Tyedmers, P. and R. Parker. 2012. Fuel consumption and greenhouse gas emissions from global tuna fisheries: preliminary assessment. ISSF Technical Report 2012-‐03. International Seafood Sustainability Foundation, McLean, Virginia, USA.
- UNEP (United Nations Environment Programme). 2000. Cleaner Production Assessment in Fish Processing. United Nations Environment Programme. www.unep.fr/shared/publications/pdf/2481-CPfish.pdf (accessed 7 February 2015)
- Ward P, Lawrence E, Darbyshire R & Hindmarsh S. 2007. Large-scale experiment shows that nylon leaders reduce shark bycatch and benefit pelagic longline fishers. Fisheries Research, 90: 100-108.
- WCPFC’s Conservation and Management Measure (CMM) 2010-07
Bigeye is a large tuna with a long, robust, and tapered body. Its pectoral fins are moderately long (22-31% of fork length) in fish larger than 110 cm fork length, but very long (30% or more of fork length) in smaller fish. It differs from yellowfin tuna (Thunnus albacares), in its colour, and by: 1) 23-31 rakers on the first gill arch (26-34 in yellowfin), 2) striated ventral surface of the liver (not striated in yellowfin), and 3) approximately equal liver lobes (in yellowfin, the right lobe is much longer than the other lobes). The second dorsal and anal fins of bigeye tuna do not grow as long as those of yellowfin tuna.
At a comparable size, the swim bladder of a bigeye tuna is larger than that of a yellowfin tuna.
The back is dark metallic blue and the sides and belly are whitish; when the fish is alive, an iridescent blue band runs along the sides. The first dorsal fin is dark yellow and the second dorsal and anal fins are pale yellow. The finlets are bright yellow with a black edge. The tail is plain and does not have a white trailing edge (as has albacore, T. alalunga).
Together with the other species of tropical tuna, bigeye tuna is near the top of the pelagic food chain. Tunas typically follow the daily vertical movement of their preferred prey (micronekton), moving to deeper habitats during the day and to shallower habitats at night. The physiology of bigeye allows them to feed deeper in the water column and for longer periods than other tropical tunas. Bigeye tuna foraging behavior also changes as they grow, with larger individuals able to more frequently use deeper habitats.
Predators of bigeye include other tunas, sharks, dolphins, sailfish, marlins, and toothed whales.
HABITAT AND DISTRIBUTION
Bigeye tuna occur worldwide in tropical and subtropical waters but are absent from the Mediterranean Sea. In the Western and Central Pacific and Indian oceans, bigeye are found between Latitudes 40º N and 40 ºS.
They are found predominantly in tropical open ocean ecoregions, in waters extending from the surface to below the mixed layer and thermocline. In coastal waters, bigeye tuna are most commonly found in waters around the bottom of the mixed layer, which varies with place and season. [See gallery for bigeye tuna distribution map and diagram]. Bigeye are rarely found over shallow coastal shelves where the ocean depth is less than about 50 m.
Despite little gene flow between populations of bigeye in the eastern and western Pacific Ocean (Philippines and Ecuador), bigeye in the Pacific Ocean appear to comprise a single Pacific-wide population. Recent analyses of bigeye tagging studies supports these genetic observations, with little mixing observed between fish tagged in the extreme east and west of the Pacific. Higher rates of mixing were observed in the central Pacific. The bigeye tuna showed little dispersal by latitude (N-S), some regional retention and some large eastward longitudinal movements. From the tagging results, three possible Pacific stocks may be inferred but for management purposes, to the present, the bigeye tuna eastern and western Pacific fisheries are assessed separately.
During mark-recapture studies, bigeye tuna in the Pacific have been recovered up to 5,372 nautical miles from their release points, after periods at liberty from one to nearly five years. In the Pacific Ocean, three types of movement patterns are identified: (1) fish that reside within 1,000 nautical miles of their release location, (2) fish that are residents, yet undertake excursions outside the residence area, to which they return, and (3) fish that are nomadic and have other movement patterns. In the Indian Ocean, tagged juveniles moved 657 nautical miles, on average, between release and recapture. In general, however, the understanding of bigeye movement and its relationship with fish size is still poor.
The higher tolerance of bigeye tuna to variation in water temperature and O2 levels allows them to use a wide range of ocean habitats. As with other tuna, the blood circulation system of bigeye tuna has a heat exchanger that rapidly lessens heating and cooling rates. This enables these fish to maintain muscle temperatures significantly above those of the environment; increasing both their swimming efficiency and the range of temperatures in which they can live. Adult bigeye tuna (>100 cm FL (fish length)) can live in water with dissolved oxygen (O2) levels as low as 1.5 ml/L and in cool water (50C - 150C). However, bigeye tuna spend little time in water temperatures below 70C and oxygen levels less than about 2 ml/L.
The characteristic daily behavior of bigeye tuna is to feed above the thermocline in the mixed layer starting at dusk, and descend below the thermocline at dawn to feed at depth in cooler waters. Bigeye tuna appear to have flexible feeding strategies, enabling them to succeed in a patchy environment. Given this flexibility, the behavior of individual fish can vary considerably with location, season, moon phase and food availability. Juvenile bigeye can school at the surface underneath floating objects, along with yellowfin and skipjack tunas. Older bigeye tuna are less commonly found near floating surface objects.
GROWTH, REPRODUCTION AND DIET
Although much is known about bigeye tuna growth, variations in growth rates between fish in different stock assessment areas and across the full size range are still under study, using several methods and sometimes integrating these: growth increments on otoliths (ear bones), tag-recapture and length frequency analysis. In the WCPO, IO and other oceans, younger bigeye tuna are relatively fast-growing but growth slows in the second year of life, when the fish are between 40 and 70 cm FL.
In the WCPO, bigeye tuna growth appears to be faster than that in other oceans up to the size of the growth slow down and slower than that in other oceans for fish at sizes larger than about 100 cm. Except for the very early growth, in the Western Indian Ocean, bigeye tuna growth rates were similar to those of bigeye tuna in the Western Pacific Ocean. The bigeye tuna in the eastern Indian and south-west Pacific oceans display different growth rates from those in the Eastern Pacific Ocean.
In the WCPO, bigeye tuna mature after 2.5 years and begin spawning at 3-4 years of age (about 100-130 cm FL, 30 Kg). Indian Ocean bigeye tuna mature at three years of age at about 100 cm FL. Maximum size is 200 cm FL, commonly to 180 cm FL, and maximum weight is 210 kg.
In the Pacific Ocean, many fish survive until 8-16 years of age. The life span of bigeye in the Indian Ocean has been estimated at 15 years.
Bigeye tuna are batch spawners, capable of spawning daily and releasing batches of about 1 to nearly 10 million eggs. The eggs and larvae are pelagic.
Bigeye spawn year-round in warm surface waters (>24°C), although spawning is generally restricted to the summer months of December to January in the tropical western Pacific and Indian oceans. However, spawning also takes place in June in the eastern Indian Ocean, and mature females are found off north-eastern Australia in August. Spawning occurs between about 30°N and 20°S in the Western Pacific. Spawning is undertaken mainly at night, between about 1900 h and 0400 h.
Bigeye tuna forage successfully, during day and night, on a range of organisms. The diet of bigeye tuna includes shallow-water squid, crustaceans and fish (mullet, sardines, small mackerels), as well as deep water micronekton (squid, euphausiids and mesopelagic fish).
GUIDE TO FURTHER READING
Note: Details of all sources are given in References below.
For bigeye tuna descriptions, see Collette 2001, Schaefer (1999), Bertrand and Josse (2000), the Indian Ocean Tuna Commission (IOTC) species identification card (http://www.iotc.org/science/species-identification-cards) and the International Game Fish Association (http://www.igfa.org/).
For the most comprehensive guides and handbooks to the identification of yellowfin and bigeye tuna, from fresh to frozen and damaged, see the Secretariat for the Pacific Community FAME Digital Library, and enter "yellowfin" AND "David Itano" (author) into the search boxes to obtain the guides, many in several languages.
For the use of habitat, see Musyl et al. (2003) and Brill et al. (2005). Predators are given in FishBase (www.fishbase.org).
For descriptions of habitat and geographic distribution, see Reygondeau et al. (2012), Collette (2001) and Lee, et al. (2005). Grewe & Hampton (1998), IOTC (2011) and Schaefer et al. (2015) address stock structures, movement and dispersion.
For information on biology, physiology and distribution, see Musyl et al. (2003), Boye et al. (2009), Lehodey et al. (2011).
For daily behavior patterns and their variability, see Evans et al. (2008) and Schaefer and Fuller (2010). For juvenile schooling behavior, see Collette (2001) and IOTC (2011).
For growth see: Lehodey et al. (1999), Farley et al (2006) and Fonteneau and Hallier (2015) on growth rates of young fish. For comparative growth rates by ocean from tagging studies, see Fonteneau and Hallier (2015); for IO growth Stéquert & Conand (2004); for WCPO and EPO, Farley et al. (2006), Nicol et al. (2011), and Fonteneau and Hallier (2015).
For information on maximum size, see Lehodey et al. (1999), Collette (2001), and Fishbase (www.fishbase.org). For life span and age information, see Farley et al. (2006), Lehodey et al. (1999), Harley et al. (2009) and IOTC (2011).
On maturation and reproduction of bigeye tuna, see Schaefer et al. (2005); for WCPO, see Lehodey et al. (1999), Farley et al. (2006), SPC (2009), and Sun et al. (2013); and for IO, see IOTC (2011). For bigeye tuna diet, see Musyl et al. (2003), Evans et al. (2008), and Collette (2001).
- Bertrand, A, and E Josse. 2000. Tuna target-strength related to fish length and swimbladder volume. ICES Journal of Marine Science: Journal du Conseil 57:1143-1146.
- Boye J, M Musyl, R Brill & H Malte. 2009. Transectional heat transfer in thermoregulating bigeye tuna (Thunnus obesus) - a 2D heat flux model. The Journal of Experimental Biology, 212:3708-3718.
- Brill RW, KA Bigelow, MK Musyl, KA Fritsches & EJ Warrant. 2005. Bigeye tuna (Thunnus obesus) behaviour and physiology and their relevance to stock assessments and fishery biology. Collective Volume of Scientific Papers of the ICCAT, 57(2):142-161.
- Collette BB. 2001. Tunas (also, albacore, bonitos, mackerels, seerfishes, and wahoo). pp 3721-3756, in K.E. Carpenter & V.H. Niem (eds), FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Vol. 6: Bony Fishes Part 4 (Labridae to Latimeriidae), Estuarine Crocodiles, Sea Turtles, Sea Snakes and Marine Mammals. Rome, FAO.
- Evans K, A Langley, NP Clear, P Williams, T Patterson, J Sibert, J Hampton & JS Gunn. 2008. Behaviour and habitat preferences of bigeye tuna (Thunnus obesus) and their influence on longline fishery catches in the western Coral Sea. Canadian Journal of Fisheries & Aquatic Sciences, 65:2427-2443.
- Farley J, NP Clear, B Leroy, TLO Davis TLO & G McPherson. 2006. Age, growth and preliminary estimates of maturity of bigeye tuna, Thunnus obesus, in the Australian region. Marine and Freshwater Research, 57: 713-724.
- Fonteneau, A, and JP Hallier. 2015. Fifty years of dart tag recoveries for tropical tuna: A global comparison of results for the western Pacific, eastern Pacific, Atlantic, and Indian Oceans. Fisheries Research 163:7-22.
- Grewe P & J Hampton. 1998. An assessment of bigeye (Thunnus obesus) population structure in the Pacific Ocean, based on mitochondrial DNA and DNA microsatellite analysis. Report, CSIRO Marine Research. 34 p.
- Harley S, S Hoyle, A Langley, J Hampton & P Kleiber. 2009. Stock assessment of bigeye tuna in the Western and Central Pacific Ocean. Western and Central Pacific Fisheries Commission Scientific Committee Fifth Regular Session, 10-21 August 2009, Port Vila, Vanuatu. WCPFC-SC5-2009/SA-WP-4. 98 p.
- IOTC (Indian Ocean Tuna Commission). 2011. Executive Summary: status of the Indian Ocean bigeye tuna (Thunnus obesus) resource. IOTC-2011-SC14-09. 9 p.
- Lee PF, IC Chen IC & WN Tzeng. 2005. Spatial and temporal distribution patterns of bigeye tuna (Thunnus obesus) in the Indian Ocean. Zoological Studies, 44(2): 260-270.
- Lehodey, P, J Hampton & B Leroy. 1999. Preliminary results on age and growth of bigeye tuna (Thunnus obesus) from the western and central pacific ocean as indicated by daily growth increments and tagging data. Standing Committee on Tuna and Billfish 12 16-23 June 1999, Tahiti. Working Paper BET-2, 18 p.
- Lehodey P, J Hampton, RW Bril, S Nicol, I Senina, B Calmettes, HO Pörtner, L Bopp, T Ilyina, JD Bell & J Sibert. 2011. Vulnerability of oceanic fisheries in the tropical Pacific to climate change. pp 433-492, in JD Bell, JE Johnson & AJ Hobday (eds), Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change. Secretariat of the Pacific Community, Noumea, New Caledonia.
- Musyl MK, RW Brill, CH Boggs, DC Curran, TK Kazama & MP Seki. 2003. Vertical movements of bigeye tuna (Thunnus obesus) associated with islands, buoys, and seamounts near the main Hawaiian Islands from archival tagging data. Fisheries and Oceanography, 12: 152-169. [abstract]
- Nicol, S, S Hoyle, J Farley, B Muller, S Retalmai, K Sisior, & A Williams. 2011. Bigeye tuna age, growth and reproductive biology (Project 35). WCPFC-SC7-2011/SA- WP -01, Revision 1 (3 August 2011).
- Reygondeau, G, O Maury, G Beaugrand, JM Fromentin, A Fonteneau & P Cury. 2012. Biogeography of tuna and billfish communities. Journal of Biogeography, 39:114-129.
- Schaefer, KM. 1999. Comparative study of some morphological features of yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tunas. Bulletin/Inter.-American Tropical Tuna Commission, 21:491-525.
- Schaefer, KM, DW Fuller, & N Miyabe. 2005. Reproductive biology of bigeye tuna (Thunnus obesus) in the eastern and central Pacific Ocean. Inter-American Tropical Tuna Commission. Bulletin 23:3-31.
- Schaefer, K & D. Fuller. 2010. Vertical movements, behavior, and habitat of bigeye tuna (Thunnus obesus) in the equatorial eastern Pacific Ocean, ascertained from archival tag data. Marine Biology 157:2625-2642.
- Schaefer, K, D Fuller, J Hampton, S Caillot, B Leroy, & D Itano. 2015. Movements, dispersion, and mixing of bigeye tuna (Thunnus obesus) tagged and released in the equatorial Central Pacific Ocean, with conventional and archival tags. Fisheries Research 161:336-355.
- SPC, OFP (Secretariat of the Pacific Community’s Oceanic Fisheries Programme). 2009. Tuna fisheries in the western and central Pacific: an update. SPC Fisheries Newsletter #129 - May/August 2009: 8-9.
- Stéquert B & F Conand F. 2004. Age and growth of bigeye tuna (Thunnus obesus) in the Western Indian Ocean. Cybium, 28:163-170.
- Sun, CL, SZ Yeh, YJ Chang, HY Chang & SL Chu. 2013. Reproductive biology of female bigeye tuna Thunnus obesus in the western Pacific Ocean. Journal of Fish Biology, 83: 250-271.
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